Important information about Hyperthermia, heat stress, heat illness, or heat stroke and how to prevent it.

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Being hot for too long can cause many illnesses that are all grouped under the name hyperthermia (hy-per-ther-mee-uh).

People Susceptible to Hyperthermia:

• Larger people as they have a decreased surface area to body volume ratio and thus a decreased heat transfer from the body.

• Obese people for the above reason and because fat is a good insulator, reducing heat loss.

• Unfit people as heat produced is dependent on the intensity of exercise, Unfit individuals work harder at a higher relative intensity to keep up with fitter players.

• Ill people or those recently unwell who have had fever, diarrhea or vomiting, will commence playing in an already dehydrated state.

• People, un-acclimated to heat will not sweat or supply blood to the skin as effectively. Therefore, ensure there has been adequate time for acclimation to the effects of heat especially people from cooler areas.

• Avoid alcohol the night before and caffeine based beverages ex. cola drinks to avoid their diuretic effects.

• Children have a reduced sweat mechanism, sweat less and sweat less precisely, and they have a higher core temperature during heat stress. They usually require longer times to acclimatize to heat. Children also have a larger surface area to body volume rations which can help heat loss but may also allow greater area for radiant heat gain.

Heat edema:

Heat edema is a swelling in your ankles and feet when you get hot. Putting your legs up should help. If that doesn’t work fairly quickly, check with your doctor.

Heat syncope:

Heat syncope is a sudden dizziness that may come on when you are active in the heat. If you take a form of heart medication known as a beta blocker or are not used to hot weather, you are even more likely to feel faint when in the heat. Putting your legs up and resting in a cool place should make the dizzy feeling go away.

Heat Stress:

Heat stress is a buildup of body heat generated either internally by muscle use or externally by the environment. Heat exhaustion and heat stroke result when the body is overwhelmed by heat. An increase in body temperature of two degrees Fahrenheit can affect mental functioning. A five degree Fahrenheit increase can result in serious illness or death. During hot weather, heat illness may be an underlying cause of injuries such as heart attacks, falls and equipment accidents. The most serious heat related illness is heat stroke. The symptoms are confusion, irrational behavior, convulsions, coma, and death. 20% of heat stroke victims die regardless of health or age. The side effects of heat stroke are heat sensitivity and varying degrees of brain and kidney damage.

Symptoms of Heat Stress

Extreme high summer temperatures causes an uncomfortable, performance hindering, and hazardous environment for workers, which is compounded by operations that require workers to wear personal protective equipment (PPE) such as semi-permeable or impermeable, chemical-resistant suits for asbestos removal and agriculture. Heat stress causes slowed reaction time, reduced energy, difficulty with coordination and attention, weakness of muscles, reduced strength during heavy physical exertion and normal day to day activities. In a work environment, there is reduced safety, risk of injury, decreased efficiency and overall loss of productivity. Let's not forget personal comfort. What's the answer? TechNiche® Cool Vest products provide great relief for all of these symptoms of heat stress.

Your body is always working to keep a balance between how much heat it makes and how much it loses. Your brain is the thermostat. It sends and receives signals to and from parts of your body that affect temperature, such as the spinal cord, muscles, blood vessels, skin, and glands that make substances known as hormones. To get rid of excess heat, the body uses two cooling mechanisms:

1) The heart rate increases to move blood -- and heat -- from heart, lungs, and other vital organs to the skin.

2) Too much heat causes sweating. When the sweat dries from your skin, the surface of your body cools and your temperature goes down. Sweating increases so that more sweat can evaporate and cool the body. Sweating is the body's most important way of dispersing excess heat. But when too much sweat is lost through heavy labor or working under hot, humid conditions, the body doesn't have enough water left to cool itself. The result is dehydration.

Too much heat is not safe for anyone. It is even riskier if you are older or if you have health problems. It is important to get relief from the heat quickly. If not, you might begin to feel confused or faint. Your heart could become stressed, and maybe stop beating. If your job (or sport) causes you to become uncomfortably warm to the point where your performance begins to lag due to heat stress, then the TechNiche® line of body cooling vests are for you. The goal of Core-Comfort.Com is to mitigate the heat stress when operating in harsh climates, increase work duration of the individual, decrease their hydration needs, and improve their mental acuity and overall comfort.

Heat exhaustion:

Heat exhaustion is a warning that your body can no longer keep itself cool. You might feel thirsty, dizzy, weak, uncoordinated, nauseated, and sweat a lot. Your body temperature stays normal, skin feels cold and clammy. Your pulse can be normal or raised. Resting in a cool place, drinking plenty of fluids, and getting medical care should help you feel better soon. If not, this condition can progress to heat stroke. For more, please read the Heat Exhaustion article.

Heat Cramps:

Heat cramps usually affect people who sweat a lot during strenuous activity. This sweating depletes the body's salt and moisture. The low salt level in the muscles causes painful cramps. Heat cramps may also be a symptom of heat exhaustion.

Recognizing Heat Cramps

Heat cramps are the painful tightening of muscles in your stomach area, arms, or legs. Cramps can result from hard work or exercise. While your body temperature and pulse usually stay normal during heat cramps, your skin may feel moist and cool. Take these cramps as a sign that you are too hot — find a way to cool your body down. Be sure to drink plenty of fluids, but not those containing alcohol or caffeine. If you have heart problems or are on a low sodium diet, get medical attention for heat cramps.

What to Do

If medical attention is not necessary, take these steps:

* Stop all activity, and sit quietly in a cool place.

* Drink clear juice or a sports beverage.

* Do not return to strenuous activity for a few hours after the cramps subside because further exertion may lead to heat exhaustion or heat stroke.

* Seek medical attention for heat cramps if they do not subside in 1 hour.

Heat Rash:

Heat rash is a skin irritation caused by excessive sweating during hot, humid weather. It can occur at any age but is most common in young children.

Recognizing Heat Rash

Heat rash looks like a red cluster of pimples or small blisters. It is more likely to occur on the neck and upper chest, in the groin, under the breasts, and in elbow creases.

What to Do

The best treatment for heat rash is to provide a cooler, less humid environment. Keep the affected area dry. Dusting powder may be used to increase comfort, but avoid using ointments or creams-they keep the skin warm and moist and may make the condition worse. Treating heat rash is simple and usually does not require medical assistance. Other heat-related problems can be much more severe.


What is thermoregulation?

Maintenance of the human body requires numerous chemical reactions that operate best at a particular Core Body temperature. We are described as homoeothermic or warm blooded and need to maintain a relatively constant core temperature for these chemical reactions, called metabolism, to occur optimally to produce efficient mechanical movement. When engaged in exercise, the body temperature is elevated as the metabolic rate increases to meet the energy demands of the work. From an efficiency view approximately 30% of metabolism is converted to mechanical work while the remaining 70% is expressed as heat. Further heat, may be gained from exposure to the sun in the form of radiant heat or convection currents. In order to preserve health and function optimally the body must find ways of dissipating this heat.

Normally resting core temperature is about 36.9°C ( -/+ 1°C ) and may reach 40°C and higher in some individuals during exercise with or without adverse effects.

There are various homeostatic mechanisms employed by the body in an attempt to maintain the core temperature within narrow limits. During, exercise there is increase blood flow to the skin—vasodilatation—to maximize heat loss. At the same time blood is diverted to the working muscles. There is therefore an inherent competition between mechanisms that maintain a large blood flow to exercising muscles and those that provide adequate thermoregulation. Body heat is lost by radiation, conduction, convection and evaporation:


Heat transfer via electromagnetic heat waves through the air.


Transfer of heat by direct air molecules around body warmed by body heat.


Heat loss via air currents moving warm air away from the body.


Evaporation of sweat from the skin surface is the most effective way to remove heat from the body. When the sweat reaches the skin it evaporates and cools the surface causing a heat transfer from the blood. The cooled blood returns to the internal body environment where it absorbs heat from the tissues and the process is repeated. Sweat does not cool the skin.


Sweat is described as a hypotonic saline solution meaning that in comparison to body fluids it is a less concentrated salt electrolyte solution. It contains over 99% water and only 0.2 to 0.4% sodium chloride—mainly sodium. When the body sweats the relative concentration of salt left in the body fluids is therefore increased. Only during exercise under extreme adverse conditions over prolonged periods are significant amounts of electrolytes lost. Normally after exercise, sufficient electrolytes replenished at meal times. The fluid in sweat comes from the extra cellular fluid of the blood plasma and that bathing the cells. Sweating therefore places demands on the body's fluid reserves and creates a relative state of dehydration.

Why is Thermoregulation important?

The primary focus of thermoregulation is of course the continued health of the individual.

However failure to control body heat will also work to the detriment of sports performance. If fluid loss exceeds replacement, dehydration can occur. This may result in decreased blood pressure, increased heart rate, decreased blood to working muscles and the skin, and subsequent decrement in exercise performance. The individual may also be at risk of developing heat illnesses, such as heat cramps, heat exhaustion and heat stroke.


Dehydration during exercise in the heat occurs primarily from sweating which causes a decrease in circulating blood volume. An associated decrease in blood pressure places stress on the cardiovascular system trying to distribute adequate blood to the working muscles and at the same time diverting blood to the skin for heat exchange. This decrease in blood volume causes the heart rate to increase in an attempt to provide blood flow needed to meet the energy demands of the exercise. As dehydration continues exercise performance and the sweat mechanism is compromised and the body temperature increases accordingly. This juggling of circulatory adjustments in an attempt to cool the body also causes early accumulation of lactic add with subsequent premature use of glycogen stores and early fatigue during exercise. Decreased blood flow to working muscles reduces the body's capacity to buffer and oxidizes lactic acid. In an attempt to maintain blood to these muscles, hepatic (liver) blood flow is lactate uptake and oxidation by the liver. Both factors are interrelated and contribute to early fatigue during even moderate exercise in the heat. Thirst and dehydration are not synonymous and thirst is a poor indicator of dehydration.

It is important therefore not to rely on voluntary drinking. At commencement of thirst a player may already be dehydrated 2 to 3%. Decrements in performance occur at all levels of dehydration and increase in magnitude as the level of dehydration increases. Fluid loss equal to 3% of body weight can cause a significant reduction in aerobic work capacity ranging/row 6% to 15%. Further fluid losses of 4% or 5% can cause declines in performance by 20% to 30%. Note that these decrements in performance may be heightened depending upon the fitness of the individual and relative conditions on the day. Fluid losses from the body can be expressed in terms of weight lost. That is for every one kilogram of weight lost during exercise one liter of fluid has been lost—adjusted for any intake of fluid or urine voided.

I kg weight lost = 1 liter body fluid lost.

Heat Illness:

The most important issues of thermoregulation concern the health of the individual in avoidance of hyperthermia and associated heat illness. The major forms of heat illness in order of severity are heat cramps, heat exhaustion and heat stroke. "There is often no clear-cut demarcation between overlap. When heat illness does occur however, immediate action must be taken to reduce the heat stress and re-hydrate the person until medical help is available.” Heat Cramps or involuntary muscle spasms usually occur in the specific muscles exercised after prolonged intense work. Body temperature may or may not be elevated. They are thought to occur as a result of water loss rather than salt depletion, causing an imbalance in the body's electrolyte concentrations. Heat exhaustion can develop in un-acclimated individuals early in the season during hot humid weather. Exercise-induced heat exhaustion is believed to occur due to ineffective circulatory adjustments and depletion of extra-cellular fluid—particularly blood plasma volume—from excess sweating. Blood tends to pool in the periphery due to the dilated blood vessels markedly reducing central blood volume and cardiac output.

Therefore the cardiovascular system struggles to adequately meet the body's needs.

Signs and Symptoms of heat illness:

Signs and symptoms of heat illness include extreme fatigue, weak, rapid pulse, low blood pressure in an upright position, headache, and dizziness, Sweating may be reduced and body temperature elevated to 39°C but not above dangerous levels around 40°C. A person suffering these symptoms should cease activity and rest in a cool environment. Heat exhaustion can deteriorate into heat stroke if allowed to progress. Summon medical assistance A.S.A.P. If conscious, fluids should be administered orally but if unconscious an intravenous feed of saline is recommended.

Heat Stroke:

Heat stroke is an emergency — it can be life threatening! You need to get medical help right away. Getting to a cool place is very important, but so is treatment by a doctor. Many people die of heat stroke each year. Older people living in homes or apartments without air conditioning or good airflow are at most risk. So are people who don’t drink enough water or those with chronic diseases or alcoholism.

Heat Stroke is the most serious and complex heat stress malady and requires immediate medical attention. Heat stroke is caused by failure of the in excessively high body temperature which is life threatening. The sweating response normally shuts down and the skin is dry and hot, body temperature rises to 4l.5°C or higher and severe strain is placed on the circulatory system. However there have been instances reported where some individual’s body temperature has only reached 39°C during heat stroke and in others where sweating has continued to occur so the skin presents as wet and not dry.

This may occur particularly when the relative humidity is high which prevents the evaporation of sweat from the skin.

This highlights the importance of recognizing the peculiarities amongst individuals and not fall prey to recipe diagnosis and treatment. Because heat stroke is a medical emergency aggressive steps need to be taken whilst awaiting medical treatment.

The elevated core temperature needs to be rapidly reduced as mortality is related to both the magnitude and duration of hyperthermia. Immediate treatment may include alcohol rubs, fans, cool baths and ice parks but do not promote shivering—shivering promotes an unwanted increase in body heat.

Oral temperature is often highly inaccurate due to the heightened pulmonary ventilation—increased breathing—during and immediately post exercise. The oral temperature is therefore influenced by the evaporative cooling effect in the mouth from passing air currents. Rectal temperature is far more accurate. When exerting yourself in the heat, if you suddenly feel chilled and goose bumps form on your skin, stop exercising, get into a cool environment and drink plenty of cool fluids. The body's thermoregulation system has become confused and thinks that the body temperature needs to increase even more! Left untreated this condition can lead to heat stroke and death.

The Signs of Heat Stroke

* Fainting, possibly the first sign,

* Body temperature over 104° F,

* A change in behavior — confusion, being grouchy, acting strangely, or staggering,

* Dry flushed skin and a strong rapid pulse or a slow weak pulse,

* Not sweating, despite the heat, acting delirious, or being in a coma.

Who Is at Risk?

Hundreds of people die from hyperthermia each year during very hot weather. Most are over 50 years old. The temperature outside or inside does not have to hit 100° F for you to be at risk for a heat-related illness. Health problems that put you at risk include:

* Heart or blood vessel problems, poorly working sweat glands, or changes in your skin caused by normal aging.

* Heart, lung, or kidney disease, as well as any illness that makes you feel weak all over or causes a fever.

* High blood pressure or other conditions that make it necessary for you to change some of the foods you eat. For example, if you are supposed to avoid salt in your food, your risk of heat-related illness may be higher. Check with your doctor.

* Conditions treated by drugs such as diuretics, sedatives, tranquilizers, and some heart and blood pressure medicines. These may make it harder for your body to cool itself by perspiring.

* Taking several drugs for a variety of health problems. Keep taking your prescriptions, but ask your doctor what to do if the drugs you are taking make you more likely to become overheated.

* Being quite a bit overweight or underweight.

* Drinking alcoholic beverages.

What are the risk factors?

Relative Humidity and Heat:

The amounts of relative humidity and heat on the day are extremely important. The humidity is the amount of water vapor carried in the air relative to its carrying capacity at a given temperature. This bulb temperature and is most significant with regard to thermoregulation. Playing or training when the wet bulb temperature is high—hot humid conditions— reduces the temperature gradient between skin and air and the sweat tends to pool on the surface of the body. Hence there is little chance for the sweat to evaporate and the body quickly overheats.

Type and Color of Clothing:

Tight fitting clothing does not allow air flow to assist in evaporative or convective cooling. Similarly clothing that does not "breathe" for example, nylon and polyester, does not allow absorption and removal of sweat. Instead they promote a warm layer of fluid between the garment and body similar to the diving wetsuit. Dark colors attract more heat especially black jerseys. Black reflects no color and therefore absorbs all light and heats up significantly. On the other hand white reflects all the colors and is much cooler.


Hydration is the absorption of fluid into the body and water is the most popular medium. The aim is to replace the level of body fluids lost mainly through sweat although this is seldom possible during exercise in adverse conditions. It is important therefore that all attempts are made to replace as much fluid as possible and not to rely on voluntary drinking. On hot days, hydration should commence well before activity starts and continue during and after cessation. In extreme heat, hydration should commence the night prior. On relatively cool or cold days, hydration can be commenced 5-10 minutes prior to beginning activity, provided the individual is hydrated, i.e. normally hydrated. Clear urine is a broad indicator of an adequate level of hydration but fluid should be replaced after voiding. The rate of gastric emptying from the stomach to the small intestine is important as very little water is absorbed via the stomach itself. The gastric emptying rate of plain water is about I liter per hour for adults at rest, i.e. 250ml/15 minutes— but can vary. Cool to cold fluids tend to empty more rapidly, may help reduce core temperature and are generally more palatable. In order to prevent dehydration and gastric distress, a basic guideline for adults would be the consumption of 400 to 600 ml of fluid either immediately before or 10 to 15 minutes prior to activity and then regular ingestion of 150 to 250 ml of fluid at 15 minute intervals during activity may be required depending upon the conditions on the day.

Determining Sweat Rate:

Due to the dehydration/thirst anomaly, a hydration plan should be adopted and calculated on individual sweat rates during activity. Under different work conditions sweat rates can vary from I liter per hour to as much as 3 to 4 liters per hour under extreme conditions. The rates can also vary widely amongst Individuals: A good estimate of sweat loss can be made by comparing the pre and post training body weights over time. Ensure corrections are made for ingested fluid during training and any urine excreted.

Water or sports drink?

Water is the universal medium and is usually hypotonic. As mentioned earlier, sweat is also hypotonic. During activity, dehydration progresses and the concentration of electrolytes in the body fluids become progressively more concentrated. Therefore the need to replace body water is greater than the need for electrolytes because, only by replacing water is the concentration of electrolytes returned to normal. Given that ingested fluid in the gut is technically outside the body, an isosmotic or hypotonic solution would be the favored hydration medium.

Sports Drink:

Sports drinks offer dual advantages of hydration and carbohydrate feeding to delay fatigue. Past scientific findings did not support exogenous carbohydrate feedings to sustain mixed anaerobic and aerobic activities. Recent studies however have supported delayed onset of fatigue with supplementation of such feeding's during exhaustive repetitive bouts of anaerobic activity. Enhanced performance has been linked to maintenance of blood glucose and sparing of liver glycogen levels, increased muscle glucose and possible increase in muscle glycogen levels. Some research suggests that a sports drink with a low concentration of an electrolyte and carbohydrate solution has advantages over plain water as a re-hydration medium. Commercially prepared sports drinks containing 6% carbohydrate, preferably a glucose polymer, with 20mm of sodium per liter are typically preferable. These fluids are absorbed relatively quickly and promote greater fluid retention post activity through reduced urine production. The current recommendation is to avoid solutions of carbohydrate greater than 8% concentration to reduce the temporary shift of fluid into the gut and decreased rate of gastric emptying.

Similarly electrolyte concentration should be kept to a minimum to avoid further temporary dehydration due to the lower concentration of sweat relative to body fluids. The improved palatability of sports drinks tends to enhance voluntary drinking compared to water both during and post activity varies between individuals. When assessing palatability one should appreciate that perception of taste changes at rest compared to exercise.


The information in this website is of a general nature. Individual circumstances may require modification of general advice from an appropriate health professional eg Doctor.

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